This project is concerned with an analysis of the activity of nerve cells in that system within the primate brain which is necessary and responsible for the process we refer to as attention. Monkeys trained to perform visually-guided go, no-go discrimination tasks are tested whilst extracellular recordings are made from brain regions thought to be part of an attentional system. The most recent study in this series examined structures in the forebrain. The exploration of the frontal cortex has been completed. Current work investigates attention-related activity in posterior parietal and extrastriate cortices.